Apparatus for recording and reproducing charge latent image

ABSTRACT

A charge latent image is formed on a recording medium in response to information and a reference pattern so that the information and the reference pattern are recorded on the recording medium. During a reproducing process, the information is read out from the recording medium and an information signal representing the readout information is generated. In addition, the reference pattern is read out from the recording medium and a reference signal representing the reference pattern is generated. The information is demodulated from the information signal. The reference signal is used in the demodulation of the information from the information signal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 347,640, filedMay 5, 1989.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus for recording and reproducing acharge latent image.

In some image recording systems, a photoelectric transducer sectionenables a charge storage member to be charged in accordance with anoptical image of an object and thereby allows a charge latent image tobe formed on the charge storage member. The distribution of an electricsurface potential of the charge storage member represents the opticalimage. In some reproducing systems, a surface potential sensor of anelectrostatic induction type is used in detecting the distribution ofsuch an electric surface potential and generating a correspondingelectric signal.

Generally, during the detection of a surface potential distribution of acharge latent image, the charge latent image is scanned by the surfacepotential sensor. In some cases, an output signal from the surfacepotential sensor is contaminated by error components which relate to thepositional relation between the surface potential sensor and the chargelatent image. It is desirable to compensate for such error components.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an excellent recording andreproducing apparatus using a charge latent image.

According to a first aspect of this invention, an apparatus forrecording and reproducing a color image via a charge latent imagecomprises an optical filter including a color separation section and anindex section, the color separation section including recurrent groupseach having stripes of at least three different colors, the indexsection including a pattern related to a period of the recurrent groupsin the color separation section; a photoconductive member; a recordingmember; means for focusing an optical image on the photoconductivemember via the filter; means for forming a charge latent image on therecording member in response to the optical image on the photoconductivemember, the charge latent image having a color information regioncorresponding to the color separation section of the filter and an indexregion corresponding to the index section of the filter; means fordetecting the charge latent image on the recording member; means forgenerating a color information signal in accordance with the detectedcharge latent image related to the color information region; means forgenerating an index signal in accordance with the detected charge latentimage related to the index region; and means for demodulating colorinformation from the generated color information signal on the basis ofthe generated index signal.

According to a second aspect of this invention, an apparatus forrecording and reproducing a color image via a charge latent imagecomprises an optical filter including a color separation section and anindex section, the color separation section including recurrent groupseach having parallel stripes of at least three different colors, theindex section including a pattern of parallel stripes extending parallelto the stripes in the color separation section, the pattern beingrelated to a period of the recurrent groups in the color separationsection; a photoconductive member; a recording member; means forfocusing an optical image on the photoconductive member via the filter;means for forming a charge latent image on the recording member inresponse to the optical image on the photoconductive member, the chargelatent image having a color information region corresponding to thecolor separation section of the filter and an index region correspondingto the index section of the filter; means for scanning the charge latentimage in a main scanning direction approximately corresponding to alongitudinal direction of the stripes in the filter and scanning thecharge latent image in a sub scanning direction substantiallyperpendicular to the main scanning direction to sequentially detectsegments of the charge latent image on the recording member, and forgenerating a first signal sequentially representing the detectedsegments of the charge latent image, wherein the detected segmentsrepresented by the first signal are ordered on a time axis along adirection corresponding to the main scanning direction; means forconverting the first signal into a second signal sequentiallyrepresenting the detected segments of the charge latent image, whereinthe detected segments represented by the second signal are ordered on atime axis along a direction corresponding to the sub scanning direction;means for generating a color information signal on the basis of thesecond signal representing the detected segments of the charge latentimage which relate to the color information region; means for generatinga reference signal on the basis of the second signal representing thedetected segments of the charge latent image which relate to the indexregion; and means for demodulating color information from the generatedcolor information signal on the basis of the generated reference signal.

According to a third aspect of this invention, an apparatus forrecording and reproducing a charge latent image comprises means forforming a charge latent image on an information region of a recordingmedium in response to information and recording the information into theinformation region of the recording medium; means for forming a chargelatent image on a reference region of the recording medium in responseto a positional reference pattern and recording the positional referencepattern into the reference region of the recording medium, the referenceregion extending along a side of the information region; means forreading out the information from the recording medium and generating aninformation signal representing the readout information; means forreading out the positional reference pattern from the recording mediumand generating a corrective signal on the basis of the readoutpositional reference pattern, wherein the corrective signal depends on apositional relation between the recording medium and the informationreading means; and means for correcting the generated information signalin accordance with the corrective signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a recording system according to a firstembodiment of this invention.

FIG. 2 is a plan view of part of the color separation filter in FIG. 1.

FIG. 3 is a diagram of a reading device in the first embodiment.

FIG. 4 is a timing diagram showing the waveforms of an input signal andoutput signals into and from the shift register of FIG. 3.

FIG. 5 is a plan view of the reading device and the recording medium inthe first embodiment.

FIG. 6 is a diagram related to the processing of the output signal fromthe reading device in the first embodiment.

FIG. 7 is a diagram of the output signal from the reading device in thefirst embodiment.

FIG. 8 is a diagram showing a manner of the signal write into and thesignal read from a memory in the first embodiment.

FIG. 9 is a diagram showing the relation between the index signal andthe color information signal in the first embodiment.

FIG. 10 is a diagram showing the positional relation between a colorseparation filter and scanning directions in a case different from thatof FIG. 6.

FIG. 11 is a diagram showing the relation between the index signal andthe color information signal in the case of FIG. 10.

FIG. 12 is a block diagram of a circuit for processing the output signalfrom the reading device in the first embodiment.

FIG. 13 is a block diagram of a color demodulation circuit in the firstembodiment.

FIG. 14 is a diagram of a recording system according to a secondembodiment of this invention.

FIG. 15 is a plan view of the recording medium of FIG. 14.

FIG. 16 is a plan view of the optical mask of FIG. 14.

FIG. 17 is a plan view of the reading device and the recording medium inthe second embodiment.

FIG. 18 is a diagram of the waveforms of the reference signals in thesecond embodiment.

FIG. 19 is a block diagram of a circuit for processing the outputsignals from the reading device in the second embodiment.

FIG. 20 is a diagram of the reading device and the recording medium inthe second embodiment.

FIG. 21 is a diagram showing the contents of the color informationoutput signal from the analog-to-digital converter in the secondembodiment.

FIG. 22 is a diagram showing the positional relation between the readingdevice and the image forming region of the recording medium which occursduring the scan of the charge latent image.

FIG. 23 is a block diagram of a circuit for processing output signalsfrom a reading device in a third embodiment of this invention.

FIG. 24 is a block diagram of a circuit for processing output signalsfrom a reading device in a fourth embodiment of this invention.

FIG. 25 is a diagram showing the levels of the electric potentials whichare induced at the respective sensing electrodes when the reading deviceinclines relative to the recording medium as shown in FIG. 20.

Like and corresponding elements are denoted by the same referencecharacters throughout the drawings.

DESCRIPTION OF THE FIRST PREFERRED EMBODIMENT

FIG. 1 shows a system for recording a charge latent image on a recordingmedium RM. A scene of an object O is focused by a lens L on a recordinghead (a writing head) WH which generates a charge latent image on therecording medium RM in correspondence with the scene of the object O.

The recording medium RM has a laminated structure including a chargelatent image forming layer CHL and an electrode layer E. The electrodelayer E functions as a base plate of the recording medium RM. The imageforming layer CHL is made of highly insulating material.

The recording head WH has a laminated structure including a transparentelectrode layer Et, a color separation filter layer Fst, and aphotoconductive layer PCL. The photoconductive layer PCL of therecording head WH opposes the latent image forming layer CHL of therecording medium RM.

The positive terminal of a dc power source Vb is electrically connectedto the electrode layer E of the recording medium RM. The negativeterminal of the dc power source Vb is electrically connected to theelectrode layer Et of the recording head WH. The combination of theelectrode layers E and Et, and the dc power source Vb functions to applyan electric field to a region between the electrode layers E and Etwhich accommodates the photoconductive layer PCL of the recording headWH.

An optical image of the object O is focused by the lens L on thephotoconductive layer PCL of the recording head WH through thetransparent electrode layer Et and the color separation filter layer Fstof the recording head WH. The electric resistance of the photoconductivelayer PCL of the recording head WH varies in accordance with the focusedoptical image of the object O so that a charge latent image is formed onthe image forming layer CHL of the recording medium RM in correspondencewith the optical image of the object O as disclosed in European patentapplication No. 89300633.8 by the same applicant.

The recording medium RM may have any one of various shapes such as adisk shape, a tape shape, a sheet shape, and a card shape.

As shown in FIG. 2, the color separation filter Fst has an index regionZs and an image information region Zc. In the index region Zs, opaquestripes 2 and transparent stripes 3 are alternately arranged inparallel. A pair of the opaque stripe 2 and the transparent stripe 3corresponds to one period of an index signal which will be describedlater. The image information region Zc has recurrent groups eachcomposed of parallel stripes 4, 5, and 6 of red (R), green (G), and blue(B). The stripes 4, 5, and 6 of the image information region Zc extendin parallel with the stripes 2 and 3 of the index region Zs. The widthof one group of the color stripes 4, 5, and 6 in the image informationregion Zc is equal to the width of a pair of the stripes 2 and 3 of theindex region Zs.

As shown in FIG. 5, the charge latent image formed on recording mediumRM has an index portion Zs1 and an effective portion Zc1 whichcorrespond to the index region Zs and the image information region Zc ofthe color separation filter Fst respectively. Specifically, the indexportion Zs1 of the charge latent image is composed of an alternatearrangment of "black" stripes corresponding to the opaque stripes 2 ofthe color separation filter Fst and "white" stripes corresponding to thetransparent stripes 3 of the color separation filter Fst. Incorrespondence with the color stripe arrangement of the imageinformation region Zc of the color separation filter Fst, the effectiveportion Zc1 of the charge latent image is divided into recurrent groupseach composed of stripes corresponding to red (R), green (G), and blue(B) respectively.

FIG. 3 shows a reading device EDA which is used in detecting a chargelatent image on the recording medium RM. The reading device EDA hassensing electrodes ED1-EDn which are connected to the gates of detectingfield-effect transistors DFfg1-DFfgn via connection lines l1-lnrespectively. The detecting transistors DFfg1-DFfgn are of thefloating-gate MOS type. The drains of the detecting transistorsDFfg1-DFfgn are connected in common to a power supply line V. Thesources of the detecting transistors DFfg1-DFfgn are connected to thedrains of switching field-effect transistors SF1-SFn respectively. Thesources of the switching transistors SF1-SFn are connected in common toan output terminal 7. A load resistor Rl is connected between the outputterminal 7 and the ground.

The switching transistors SF1-SFn serve as switches connecting anddisconnecting the detecting transistors DFfg1-DFfgn to and from theoutput terminal 7. In each of the switching transistors SF1-SFn, thesource-drain path is made conductive and nonconductive when the gatereceives a high level voltage and a low level voltage respectively. Inother words, each of the switching transistors SF1-SFn is made on andoff when its gate receives a high level voltage and a low level voltagerespectively.

The gates of the switching transistors SF1-SFn are connected torespective output terminals of a shift register SR and are thussubjected to output signals P1-Pn from the shift register SR. A clockterminal of the shift register SR receives a clock signal Pc via a clockinput terminal 8, the clock signal Pc taking a waveform as shown in FIG.4.

As shown in FIG. 4, the output signals P1-Pn from the shift register SRsequentially assume high levels in response to the input clock signalPc. Accordingly, the switching transistors SF1-SFn are sequentially madeon in accordance with the clock signal Pc.

As shown in FIG. 5, the reading device EDA has a straight elongate body.The sensing electrodes ED1-EDn are arranged in a line along the body ofthe reading device EDA. The reading device EDA is placed close to therecording medium RM. In general, the reading device EDA is set inparallel to the horizontal direction X (also referred to as the mainscanning direction X) of the image-holding square region of therecording medium RM. Accordingly, the line of the sensing electrodesED1-EDn extends in parallel to the horizontal direction X. The recordingmedium RM is previously charged in correspondence with an optical imageof the object O and thus has a charge latent image. The distribution ofan electric surface potential at a recording surface of the recordingmedium RM represents the charge latent image. The sensing electrodesED1-EDn are opposed to the recording surface of the recording medium RM.By electrostatic induction, the sensing electrodes ED1-EDn are subjectedto voltages corresponding to surface potentials of portions of therecording medium RM which oppose the sensing electrodes ED1-EDnrespectively. The induced voltages are transmitted from the sensingelectrodes ED1-EDn to the gates of the detecting transistors DFfg1-DFfgnvia the connection lines l1-ln respectively.

The switching transistors SF1-SFn are sequentially made on. Accordingly,voltage signals corresponding to the voltages of the gates of thedetecting transistors DFfg1-DFfgn are sequentially transmitted from thesources of the detecting transistors DFfg1-DFfgn to the output terminal7 via the source drain paths of the switching transistors SF1-SFn. Thus,an output signal generated at the output terminal 7 has time-domainvariation which corresponds to the distribution of the surface potentialof the horizontal linear portion of the recording medium RM. In thisway, a linear portion of the charge latent image is scanned in atime-dependent manner.

A suitable drive mechanism (not shown) moves the reading device EDArelative to the recording medium RM along the vertical direction Y (alsoreferred to as the sub scanning direction Y) of the image-holding squareregion of the recording medium RM. This vertical movement of the readingdevice EDA is suitably combined with the previously-mentioned linearscanning of the charge latent image, so that the charge latent image istwo-dimensionally scanned in a line-by-line manner. Thus, the outputsignal from the reading device EDA has a time-domain variationrepresentative of the two-dimensional distribution of the surfacepotential on the recording medium RM which corresponds to the chargelatent image. As a result of the two-dimensional scanning of the chargelatent image, the output signal from the reading device EDA sequentiallyrepresents first lines corresponding to respective pairs of the stripes2 and 3 in the index region Zs of the color separation filter Fst andsecond lines corresponding to respective groups of the color stripes 4-6in the image information region Zc of the color separation filter Fst.

During the fabrication of the reading device EDA, a semiconductorsubstrate (not shown) is formed with a pattern corresponding to thesensing electrodes ED1-EDn, the connection lines l1-ln, the detectingtransistors DFfg1-DFfgn, and other devices. The pattern-formed substrateis coated with an insulating film of suitable material such as silicondioxide to seal the sensing electrodes ED1-EDn, the connection linesl1-ln, the detecting transistors DFfg1-DFfgn, and other devices. Thissealing structure enables reliable operation of the reading device EDA.

FIG. 6 shows operating conditions of the reading device EDA in which thedirection of the line of the sensing electrodes ED1-EDn exactly agreeswith the longitudinal direction X of the stripes 2-6 of the colorseparation filter Fst, and the sensing electrodes ED1-EDn are movedexactly along the direction Y perpendicular to the direction X. Underthese conditions, unwanted crosses between different colors areprevented.

As shown in FIG. 7, one line of the output signal from reading deviceEDA has n pixels corresponding to the respective sensing electrodesED1-EDn. The output signal from the reading device EDA is sequentiallystored into a memory in a manner as shown by the "write" arrows in thepart (b) of FIG. 8. The part (a) of FIG. 8 shows the arrangement ofportions of the stored signal in the memory. In the part (a) of FIG. 8,the characters L1-Lm denote the respective line portions of the storedsignal, and the characters ED1-EDn denote the respective portions of thestored signals which are obtained via the respective sensing electrodesED1-EDn. One period in the part (a) of FIG. 8 corresponds to one periodin FIG. 6 which is an interval extending along the sub scanningdirection Y. In FIG. 6, the arrow lines (1)-(n) and (1)'-(n)' denoteintervals or distances which are travelled by the sensing electrodesED1-EDn during one period. Since one period corresponds to a pair of thestripes 2 and 3 in the index region Zs of the color separation filterFst or a group of the color stripes 4-6 in the image information regionZc of the color separation filter Fst, the signal portions correspondingto m lines are stored into the memory during one period as shown in thepart (a) of FIG. 8 where the letter m denotes an integer greater thanthree.

For example, the number n of the sensing electrodes ED1-EDn is 512, andthe reading device EDA outputs a signal corresponding to 12 (=m) linesduring the movement of the reading device EDA along the sub scanningdirection Y through an interval corresponding to one period.

The portions of the stored signal, the number of which data equals theproduct nXm of the number n of the sesing electrodes by the number m ofthe lines per one period, are read out from the memory in a sequence asexpressed by the "read" arrows in the part (b) of FIG. 8. In this case,as shown in the part (a) of FIG. 9, the readout signal portionscorresponding to the index portion Zs1 of the charge latent image forman index signal Zs2 having a reference period. In addition, the readoutsignal portions corresponding to the effective portion Zc1 of the chargelatent image form a color information signal Zc2 including a recurrentsequence of red (R), green (G), and blue (B) point signals. The signalcomponents (1)-(n) and (1)', (2)', (3)', . . . in the part (a) of FIG. 9are generated in correspondence with the intervals (1)-(n) and (1)'-(n)'of FIG. 6. The part (b) of FIG. 9 illustrates the color informationsignal Zc2 in a manner as to make clear the relation in period betweenthe color information signal Zc2 and the index signal Zs2. As understoodfrom the parts (a) and (b) of FIG. 9, the index signal Zs2 can be usedas a color demodulating carrier (a carrier for synchronous detection) ofthe red, green, and blue point signals.

FIG. 10 shows the positional relation between the color separationfilter Fst and the scanning directions X and Y in a case where thereading device EDA is set so that the direction of the line of thesensing electrodes ED1-EDn deviates from the longitudinal direction ofthe stripes 2-6 of the color separation filter Fst. The sub scanningdirection Y is perpendicular to the longitudinal direction of thestripes 2-6 of the color separation filter Fst.

In respect of the index portion of the charge latent image whichcorresponds to the index region Zs of the color separation filter Fs,reading-device output-signal portions generated in correspondence withrespective periods (1), (2), (3), . . . of FIG. 10 are converted intorespective memory output signals (1), (2), (3), . . . of FIG. 11 whichcompose an index signal. In respect of the effective region of thecharge latent image which corresponds to the image information region Zcof the color separation filter Fst, reading-device output-signalportions generated in correspondence with respective periods (1)', (2)',(3)', . . . of FIG. 10 are converted into respective memory outputsignals (1)', (2)', (3)', . . . of FIG. 11 which include respectivegroups of red (R), green (G), and blue (B) point signals. As understoodfrom FIG. 11, the waveforms of the index signal portions have a definiterelation with the sequential arrangements of the color point signals inFIG. 11, so that the index signal portions (1), (2), (3), . . . can beused as color demodulating carriers of respective color point signalgroups (1)', (2)', (3)', . . . . In this case, unwanted crosses betweendifferent colors can be prevented although the main scanning direction Xdeviates from the longitudinal direction of the color stripes of thecolor separation filter Fst.

As shown in FIG. 12, the output signal from the reading device EDA isapplied to an analog-to-digital converter ADC via the output terminal 7and is converted by the converter ADC into a corresponding digitalsignal. The digital output signal from the converter ADC is fed to amovable contact 10 of a switch SW1. The switch SW1 has three fixedcontacts 11, 12, and 13. The movable contact 10 is connected to one ofthe fixed contacts 11-13 in accordance with a switch control signalapplied via a terminal 9. The fixed contacts 11, 12, and 13 areconnected to memories MAs, MAc1, and MAc2 respectively.

When the index portion Zs1 of the charge latent image is scanned by thereading device EDA, the movable contact 10 is connected to the fixedcontact 11 of the switch SW1 so that the digital output signal from theconverter ADC is written into the memory MAs via the switch SW1. In thisway, a digital index signal is stored into the memory MAs. When theeffective portion Zc1 of the charge latent image is scanned by thereading device EDA, the movable contact 10 is connected to one of thefixed contacts 12 and 13 of the switch SW1 so that the digital outputsignal from the converter ADC is written into one of the memories MAc1and MAc2 via the switch SW1.

The relation between the operations of the memories MAc1 and MAc2 isdesigned as follows. When the digital output signal from the converterADC is written into one of the memories MAc1 and MAc2, thepreviously-stored digital signal is read out from the other of thememories MAc1 and MAc2. The digital signals corresponding to respectiveperiods are alternately stored into the memories MAc1 and MAc2, and thestored signals corresponding to respective periods are alternately readout from the memories MAc1 and MAc2. For example, the digital signalscorresponding to one period I of FIG. 10 are stored into the memoryMAc1, and the digital signals corresponding to the next one period II ofFIG. 10 are stored into the other memory MAc2.

The signal write into and the signal read from the memories MAs, MAc1,and MAc2 is designed in a manner as illustrated in the part (b) of FIG.8. An address signal generator 32 feeds address signals to the memoriesMAs, MAc1, and MAc2. A control circuit (not shown) feeds write/readcontrol signals to the memories MAs, MAc1, and MAc2. The signal writeinto and the signal read from the memories MAs, MAc1, and MAc2 arecontrolled by the address signals, and the write/read control signals.In respect of the memories MAs, MAc1, and MAc2, storage locations intowhich the digital signal is written and storage locations from which thedigital signal is read out are controlled by the address signals.

While the movable contact 10 remains disconnected from the fixed contact11 of the switch SW1, the digital index signal is read out from thememory MAs and is then fed to a digital-to-analog converter DACs1 and a90-degree phase shifter 33. The converter DACs1 derives an analog colordemodulating reference signal S1 from the input digital signal. Thephase shifter 33 shifts the phase of the input digital signal by 90degrees and outputs a phase-shifted digital signal to adigital-to-analog converter DACs2. The converter DACs2 derives an analogcolor demodulating reference signal S2 from the input phase-shifteddigital signal. The reference signals S1 and S2 are in a quadraturerelation with each other. The converters DACs1 and DACs2 outputs thereference signals S1 and S2 to output terminals 18 and 19 respectively.

The memory MAc1 is connected to a fixed contact 14 of a switch SW2. Thememory MAc2 is connected to another fixed contact 15 of the switch SW2.A movable contact 16 of the switch SW2 is connected to one of the fixedcontacts 14 and 15 in accordance with a switch control signal fed via aterminal 17. The movable contact 16 of the switch SW2 is connected to adigital-to-analog converter DACc.

The change of the switch SW2 has a predetermined timing relation withthe change of the switch SW1 as described later. When the movablecontact 10 is connected described later. When the movable contact 10 isconnected to the fixed contact 12 of the switch SW1, the movable contact16 is connected to the fixed contact 15 of the switch SW2. When themovable contact 10 is connected to the fixed contact 13 of the switchSW1, the movable contact 16 is connected to the fixed contact 14 of theswitch SW2.

The digital color point signals are alternately read out from thememories MAc1 and MAc2 and are then fed to the converter DACc via theswitch SW2. The converter DACc converts the input color point signalsinto a corresponding analog color signal S3 and outputs the signal S3 toan output terminal 20. The analog color signal S3 has a sequence ofgroups of red, green, and blue point components ordered along the subscanning direction Y (see FIG. 10).

The analog color signal S3 is expressed by the following equation usingFourier expansion.

    S3=(Er+Eg+Eb)/3+(3/2π)(EG-EB)sinωt+(3.sup.1/2 /π){Er-(1/2)(Eg+Eb)}COSω

where the characters Er, Eg, and Eb denote red, green, and blue signalcomponents corresponding to the red, green, and blue stripes 4, 5, and 6of the color separation filter Fst respectively, and ω=2πf (thecharacter "f" denotes a spatial frequency of the color stripe grouprecurrence in the color separation filter Fst). The first term of theright-hand side of the above equation denotes low frequency componentscorresponding to luminance components. The second and third terms of theright-hand side of the above equation denote high frequency componentswhich result from the quadrature modulation of the carrier "ωt" with twocolor difference signals "Eg-Eb" and "Er-(Eg+Eb)/2". Accordingly, theluminance signal "R+G+B" can be obtained from the low frequencycomponents of the color signal S3, and the two color difference signals"G-B" and "R-(G+B)/2" can be obtained from the high frequency componentsof the color signal S3. Specifically, the two color difference signals"G-B" and "R-(G+B)/2" can be derived through the synchronous detectionof the high frequency components of the color signal S3 by use of thequadrature carriers "sinωt" and "cosωt".

FIG. 13 shows a color demodulation circuit. The reference signals S1 andS2, and the color signal S3 are applied to input terminals 21, 22, and23 of the color demodulation circuit respectively. The reference signalS1 is fed via a band pass filter BPF1 to a synchronous detector 24 as ademodulation carrier (a synchronous detection carrier). The referencesignal S2 is fed via a band pass filter BPF2 to a synchronous detector25 as a demodulation carrier (a synchronous detection carrier). Thecolor signal S3 is fed via a band pass filter BPF3 to the synchronousdetectors 24 and 25. In the synchronous detectors 24 and 25, the colorsignal S3 are subjected to the synchronous detections using thedemodulation carriers. A low pass filter LPF2 derives a color differencesignal "R-(G+B)/2" from an output signal from the synchronous detector24. Another low pass filter LPF3 derives another color difference signal"B-G" from an output signal from the synchronous detector 25. The colorsignal S3 is also fed to a low pass filter LPF1. The low pass filterLPF1 extracts a luminance signal "Y_(l) =(R+B+G)" from the color signalS3. A matrix circuit MTX derives primary color signals "R", "G", and "B"from the color difference signals "R-(G+B)/2" and "B-G" and theluminance signal "Yl=(R+B+G)". The primary color signals "R", "G", and"B" are outputted to output terminals 29, 30, and 31 of the colordemodulation circuit via process amplifiers 26, 27, and 28 respectively.

DESCRIPTION OF THE SECOND PREFERRED EMBODIMENT

FIG. 14 shows a system for recording a charge latent image on arecording medium RM. A scene of an object O is focused by a lens L on arecording head (a writing head) WH which generates a charge latent imageon a disk-shaped recording medium RM in correspondence with the scene ofthe object O.

The recording medium RM includes an electrode E and a charge latentimage forming member CHL. The electrode E functions as a base plate ofthe recording medium RM. The image forming member CHL is made of highlyinsulating material. The recording medium RM is rotatable about a shaft100. As shown in FIG. 15, when the recording medium RM rotates in adirection R, the charge latent image of the object O is sequentiallyrecorded on areas RZ1, RZ2, . . . of the recording medium RM.

The recording head WH has a laminated structure including a glasssubstrate or base plate BP, a transparent electrode Et, an optical maskPMP, and a photoconductive layer PCL. An electric power source (notshown) is connected between the electrode Et of the recording head WHand the electrode E of the recording medium RM to generate apredetermined electric field between the electrodes Et and E.

In a recording process, an image of the object O is formed by the lens Lon the photoconductive layer PCL of the recording head WH, the electricresistance of the photoconductive layer PCL varies in accordance withthe image intensity of the object O so that a charge latent image isformed on the member CHL of the recording medium RM in correspondencewith the image of the object O as disclosed in the European patentapplication No. 89300633.8 by the same applicant. It should be notedthat the recording medium RM may have other shapes such as a tape shape,a sheet shape, or a card shape.

As shown in FIG. 16, the optical mask PMP has a rectangular colorseparation filter Fst and an opaque region 104 surrounding the colorseparation filter Fst. Small rectangular transparent sections 108 extendin the opaque region 104 and align at equal intervals along a side ofthe color separation filter Fst. Similarly, small rectangulartransparent sections 109 extend in the opaque region 104 and align atequal intervals along the other side of the color separation filter Fst.The color separation filter Fst has recurrent groups each composed ofhorizontally-extending parallel stripes of red (R), green (G), and blue(B). The spatial frequency of the groups of the red, green, and bluestripes is equal to the spatial frequency of the transparent sections108 and 109. The vertical positions of the transparent sections 108 and109 agree with the vertical positions of the red stripes. Thetransparent sections 108 and 109 are used to generate reference signalsrepresenting positional information.

As shown in FIG. 17, in correspondence with the color stripe arrangementof the color separation filter Fst, the main portion of the chargelatent image formed on the image-forming region Rz of the recordingmedium RM is divided into recurrent groups each composed of stripesZ(R), Z(G), and Z(B) corresponding to red, green, and blue respectively.In addition, the charge latent image has a pattern of small rectangularreference sections 108P and 109P which corresponds to the pattern of thetransparent sections 108 and 109 in the color separation filter Fst. Thespatial frequency of the groups of the stripes Z(R), Z(G), and Z(B) isequal to the spatial frequency of the reference sections 108P and 109P.The vertical positions of the reference sections 108P and 109P agreewith the vertical positions of the stripes Z(R).

The charge latent image on the image forming region RZ of the recordingmedium RM is detected by a reading device EDA which includes a structuresimilar to that shown in FIGS. 3 and 5. The sensing head EDA isrelatively moved by a suitable drive mechanism (not shown) through theplane immediately above the image forming region RZ of the recordingmedium RM to scan the image forming region RZ completely. During thescan of the image forming region RZ of the recording medium RM, the lineof the sensing electrodes of the sensing head EDA is held in a directionX roughly or exactly parallel to the stripes Z(R), Z(G), and Z(B) andthe sensing head EDA is moved along a direction Y perpendicular to thestripes Z(R), Z(G), and Z(B). The direction X and the direction Y arereferred to as the main scanning direction and the sub scanningdirection respectively. During the scan of the image forming region RZof the recording medium RM, the reading device EDA generates colorinformation signals and a pair of reference signals. The colorinformation signals are generated in correspondence with the stripesZ(R), Z(G), and Z(B). The first reference signal is generated incorrespondence with the reference section 108P. The second referencesignal is generated in correspondence with the reference sections 109P.The parts (a) and (b) of FIG. 18 show the waveforms of the first andsecond reference signals respectively. As shown in FIG. 18, thereference signals have a constant period corresponding to the spatialfrequency of the reference sections 108P and 109P. As the main scanningdirection X or the direction of the line of the sensing electrodes inthe reading device EDA deviates from the horizontal direction of theimage forming region RZ of the recording medium RM, the phases of thefirst and second reference signals shift. As the reading device EDAseparates from the recording medium RM, the amplitudes of the first andsecond reference signals decrease.

With reference to FIG. 19, the line of the sensing electrodes of thereading device EDA forms a central sensing part 119 which functions todetect the color information from the stripes Z(R), Z(G), and Z(B). Thereading device EDA also has a pair of sensing parts 117 and 118extending at sides of the central sensing parts 119. The sensing parts117 and 118 are designed to detect the reference sections 108P and 109Prespectively. Each of the sensing parts 117 and 118 includes acombination of a sensing electrode and a detecting transistor.

The sensing part 119 generates a color information signal Spi incorrespondence with the stripes Z(R), Z(G), and Z(B). The colorinformation signal Spi is fed via an output terminal 7 to an automaticgain control circuit 20. The sensing parts 117 and 118 generatereference signals Sr1 and Sr2 in correspondence with the referencesections 108P and 109P respectively. The sensing parts 117 and 118output the reference signals Sr1 and Sr2 to a phase detector 129. Thereference signal Sr1 is also fed to a peak detector 128.

The peak detector 128 detects the levels of peaks of the referencesignal Sr1 which depend on the distance between the reading device EDAand the recording medium RM. The output signal from the peak detector128 is applied to a first input terminal of a differential amplifier DA.A constant dc voltage source Vs applies a predetermined referencevoltage to a second input terminal of the differential amplifier DA. Theoutput signal from the differential amplifier DA depends on thedifference between the peak levels of the reference signal Sr1 and thereference voltage, and thus represents the deviation of the actualdistance between the reading device EDA and the recording medium RM froma desired distance determined by the reference voltage. The automaticgain control circuit 120 controls the level of the color informationsignal Spi in accordance with the output signal from the differentialamplifier DA so that a color information signal of a constant level canbe generated. The level-adjusted color information signal is outputtedfrom the automatic gain control circuit 120 to an analog-to-digitalconverter ADC. The converter ADC converts the input analog colorinformation signal into a corresponding digital color informationsignal.

As shown in FIG. 20, the central sensing part 119 of the reading deviceEDA has an "n-1" number of linearly-arranged sensing electrodes ED1,ED2, . . . EDn-1. During the scan of each line, the digital colorinformation signal from the converter ADC sequentially represents colorinformation at an "n-1" number of pixels corresponding to the sensingelectrodes ED1, ED2, . . . EDn-1 as shown in FIG. 21.

The digital output signal from the converter ADC is fed to a movablecontact 10 of a switch SW1. The switch SW1 has fixed contacts 12 and 13.The movable contact 10 is connected to one of the fixed contacts 12 and13 in accordance with a switch control signal applied via a terminal 9.The fixed contacts 12 and 13 are connected to memories MAc1 and MAc2respectively. The relation between the operations of the memories MAc1and MAc2 is designed as follows. When the digital output signal from theconverter ADC is written into one of the memories MAc1 and MAc2, thepreviously-stored digital signal is read out from the other of thememories MAc1 and MAc2. The digital signals corresponding to respectiveperiods are alternately stored into the memories MAc1 and MAc2, and thestored signals corresponding to respective periods are alternately readout from the memories MAc1 and MAc2 as in the previous first embodiment.

The signal write into and the signal read from the memories MAc1 andMAc2 is designed in a manner as illustrated in the part (b) of FIG. 8.An address signal generator 32 feeds address signals to the memoriesMAc1 and MAc2. A control circuit (not shown) feeds write/read controlsignals to the memories MAc1 and MAc2. The signal write into and thesignal read from the memories MAc1 and MAc2 are controlled by theaddress signals, and the write/read control signals. In respect of thememories MAc1, and MAc2, storage locations into which the digital signalis written and storage locations from which the digital signal is readout are controlled by the address signals.

The memory MAc1 is connected to a fixed contact 14 of a switch SW2. Thememory MAc2 is connected to another fixed contact 15 of the switch SW2.A movable contact 16 of the switch SW2 is connected to one of the fixedcontacts 14 and 15 in accordance with a switch control signal fed via aterminal 17. The movable contact 16 of the switch SW2 is connected to adigital-to-analog converter DACc.

The change of the switch SW2 has a predetermined timing relation withthe change of the switch SW1 as described later. When the movablecontact 10 is connected to the fixed contact 12 of the switch SW1, themovable contact 16 is connected to the fixed contact 15 of the switchSW2. When the movable contact 10 is connected to the fixed contact 13 ofthe switch SW1, the movable contact 16 is connected to the fixed contact14 of the switch SW2.

The digital color point signals are alternately read out from thememories MAc1 and MAc2 and are then fed to the converter DACc via theswitch SW2. The converter DACc converts the input color point signalsinto a corresponding analog color signal S3. The analog color signal S3has a sequence of groups of red, green, and blue point componentsordered along the sub scanning direction Y.

As in the previous first embodiment, the analog color signal S3 has lowfrequency components corresponding to a luminance signal and highfrequency components corresponding to two color difference signals.

The color signal S3 is fed via a band pass filter BPF3 to synchronousdetectors 24 and 25. In the synchronous detectors 24 and 25, the colorsignal S3 are subjected to the synchronous detections using demodulationcarriers S1 and S2 which will be described later. A low pass filter LPF2derives a color difference signal "R-(G+B)/2" from an output signal fromthe synchronous detector 24. Another low pass filter LPF3 derivesanother color difference signal "B-G" from an output signal from thesynchronous detector 25. The color signal S3 is also fed to a low passfilter LPF1. The low pass filter LPF1 extracts a luminance signal"Yl=(R+B+G)" from the color signal S3. A matrix circuit MTX derivesprimary color signals "R", "G", and "B" from the color differencesignals "R-(G+B)/2" and "B-G" and the luminance signal "Yl=(R+B+G)". Theprimary color signals "R", "G", and "B" are outputted to outputterminals 29, 30, and 31 via process amplifiers 26, 27, and 28respectively.

The phase detector 129 generates a signal representing the difference inphase between the reference signals Sr1 and Sr2. The output signal fromthe phase detector 129 depends on the deviation of the main scanningdirection X from the longitudinal direction of the stripes Z(R), Z(G),and Z(B). The output signal from the phase detector 129 is applied tovariable delay circuits 131 and 133 as a delay control signal. Anoscillator 130 outputs a signal having a frequency which agrees with thefrequency of the groups of red, green, and blue components in the colorsignal S3. The output signal from the oscillator 130 is applied to thedelay circuit 131 and a 90-degree phase shifter 132. The phase shifter132 shits the phase of the oscillator output signal by 90 degrees andgenerates a phase-shifted signal. The output signal from the phaseshifter 132 is applied to the delay circuit 133. The output signals fromthe oscillator 130 and the phase shifter 132 have a quadrature relationwith each other. The delay circuit 131 delays the output signal from theoscillator 131 by a time determined by the output signal from the phasedetector 129. The output signal from the delay circuit 131 is applied tothe synchronous detector 24 through a band pass filter BPF1 as the colordemodulating carrier S1. The delay circuit 133 delays the output signalfrom the phase shifter 132 by a time determined by the output signalfrom the phase detector 129. The output signal from the delay circuit133 is applied to the synchronous detector 25 through a band pass filterBPF2 as the color demodulating carrier S2. As understood from theprevious description, the color demodulating sub carriers S1 and S2 arecontrolled in accordance with the deviation of the main scanningdirection X from the longitudinal direction of the stripes Z(R), Z(G),and Z(B). Therefore, the red point color information, the green pointcolor information, and the blue point color information can bereproduced accurately without any crosses therebetween.

This embodiment has the following remarkable advantage. It is nowassumed that, during the scan of the whole of the image forming regionRZ, the angle between the longitudinal direction of the reading deviceEDA and the horizontal direction of the image forming region RZ changesas shown in FIG. 22. The arrangement of the reference regions 108P and109P enables the sensing parts 117 and 118 to detect such a change ofthe angle between the longitudinal direction of the reading device EDAand the horizontal direction of the image forming region RZ, so that thereference signals Sr1 and Sr2 reflect this angle change. Therefore, thecontrol of the color demodulating carriers S1 and S2 in response to thereference signals Sr1 and Sr2 ensures accurate detection of the colorinformation regardless of such a change of the angle between thelongitudinal direction of the reading device EDA and the horizontaldirection of the image forming region RZ.

DESCRIPTION OF THE THIRD PREFERRED EMBODIMENT

FIG. 23 shows a third embodiment of this invention which is similar tothe embodiment of FIGS. 14-21 except for designs indicated hereinafter.The transparent regions 108 are omitted from the mask pattern PMP (seeFIG. 16). Therefore, the reference regions 108P (see FIG. 19) are absentfrom this embodiment. The sensing part 117 (see FIG. 19) is omitted fromthe reading device EDA.

The output signal from the sensing part 118 is fed to the peak detector128 in place of the output signal from the sensing part 117. The outputsignal from an oscillator 143 is fed to the phase detector 129 in placeof the output signal from the sensing part 117. The output signal fromthe oscillator 143 has a constant frequency and represents a referencephase.

DETAILED OF THE FOURTH PREFERRED EMBODIMENT

FIG. 24 shows a fourth embodiment of this invention which is similar tothe embodiment of FIGS. 14-21 except for designs indicated hereinafter.In the embodiment of FIGS. 14-21, under conditions where the whole ofthe working surface of the recording medium RM exhibits a constantelectric potential, when the line of the sensing electrodes ED0, ED1,ED2, . . . , EDn-1, and EDn inclines relative to the working surface ofthe recording medium RM as shown in FIG. 20, the electric potentialsinduced at the sensing electrodes ED0, ED1, ED2, . . . , EDn-1, and EDnvary as shown in FIG. 25. This embodiment has an automatic gain controlloop which is designed to operate satisfactorily regardless of whetheror not the line of the sensing electrodes ED0, ED1, ED2, . . . , ENn-1,and EDn inclines relative to the working surface of the recording mediumRM.

A peak detector 144 detects the peak levels of the reference signal Sr1and outputs the peak level signal Sr1p to a calculator 146 and an adder148. Another peak detector 145 detects the peak levels of the referencesignal Sr2 and outputs the peak level signal Sr2p to the calculator 146.The calculator generates a signal corresponding to the value"(Sr1p-Sr2p)/n" equal to the difference between the levels of thesignals Sr1p and Sr2p which is divided by the number "n" of the sensingelectrodes ED1-EDn. A multiplier 147 multiplies the output signal fromthe calculator 146 by a signal Xm which sequentially and periodicallyassumes different levels corresponding to "1", "2", . . . "n-1"respectively. The timing of the level change of the signal Xm has apredetermined relation with the timing of the selection of the sensingelectrodes ED1, ED2, . . . , EDn-1. Specifically, when the color signalSpi corresponding to the sensing electrode ED1 is inputted into theautomatic gain control circuit 120, the signal Xm assumes the levelcorresponding to "1". When the color signal Spi corresponding to thesensing electrode ED2 is inputted into the automatic gain controlcircuit 120, the signal Xm assumes the level corresponding to "2".Similarly, when the color signal Spi corresponding to the sensingelectrode EDn-1 is inputted into the automatic gain control circuit 120,the signal Xm assumes the level corresponding to "n-1". The adder 148adds the output signals from the peak detector 144 and the multiplier147 and generates a signal corresponding to the value"{(Sr1p-Sr2p)Xm/n}+Sr1p" equal to the sum of the levels of the outputsignals from the peak detector 144 and the multiplier 147. A polarityconverter 149 inverts the polarity of the output signal from the adder148 and generates a gain control signal fed to the the automatic gaincontrol circuit 120. Under conditions where the electric potentialsinduced at the respective sensing electrodes ED1, ED2, . . . , EDn-1 arevaried by the inclination of the line of the sensing electrodes ED1,ED2, . . . , EDn-1 relative to the working surface of the recordingmedium RM as shown in FIGS. 20 and 25, the automatic gain controlcircuit 120 functions to compensate this induced potential variation toderive a level-adjusted color signal.

What is claimed is:
 1. An apparatus for recording and reproducing acolor image via a charge latent image, comprising:an optical filterincluding a color separation section and an index section, the colorseparation section including recurrent groups each having stripes of atleast three different colors, the index section including a patternrelated to a period of the recurrent groups in the color separationsection; a photoconductive member; a recording member; means forfocusing an optical image on the photoconductive member via the filter;means for forming a charge latent image on the recording member inresponse to the optical image on the photoconductive member, the chargelatent image having a color information region corresponding to thecolor separation section of the filter and an index region correspondingto the index section of the filter; means for detecting the chargelatent image on the recording member; means for generating a colorinformation signal in accordance with the detected charge latent imagerelated to the color information region; means for generating an indexsignal in accordance with the detected charge latent image related tothe index region; and means for demodulating color information from thegenerated color information signal on the basis of the generated indexsignal.
 2. An apparatus for recording and reproducing a color image viaa charge latent image, comprising:an optical filter including a colorseparation section and an index section, the color separation sectionincluding recurrent groups each having parallel stripes of at leastthree different colors, the index section including a pattern ofparallel stripes extending parallel to the stripes in the colorseparation section, the pattern being related to a period of therecurrent groups in the color separation section; a photoconductivemember; a recording member; means for focusing an optical image on thephotoconductive member via the filter; means for forming a charge latentimage on the recording member in response to the optical image on thephotoconductive member, the charge latent image having a colorinformation region corresponding to the color separation section of thefilter and an index region corresponding to the index section of thefilter; means for scanning the charge latent image in a main scanningdirection approximately corresponding to a longitudinal direction of thestripes in the filter and scanning the charge latent image in a subscanning direction substantially perpendicular to the main scanningdirection to sequentially detect segments of the charge latent image onthe recording member, and for generating a first signal sequentiallyrepresenting the detected segments of the charge latent image, whereinthe detected segments represented by the first signal are ordered on atime axis along a direction corresponding to the main scanningdirection; means for converting the first signal into a second signalsequentially representing the detected segments of the charge latentimage, wherein the detected segments represented by the second signalare ordered on a time axis along a direction corresponding to the subscanning direction; means for generating a color information signal onthe basis of the second signal representing the detected segments of thecharge latent image which relate to the color information region; meansfor generating a reference signal on the basis of the second signalrepresenting the detected segments of the charge latent image whichrelate to the index region; and means for demodulating color informationfrom the generated color information signal on the basis of thegenerated reference signal.